Secure chat service Wickr has launched a tool that allows private images to appear as cat pictures to those Facebook friends you'd rather keep in the dark. The new self-destructing photo feature, dubbed Wickr Timed Feed (WTF), lets users share photos within a Wickr feed (left)

They can also share these with their friends on Facebook – but only with up to 151 people for 24 hours.

Everybody else who is not on the 'secure list' will instead see a picture of a cat in their feed.

Wickr has been downloaded more than five million times in 196 countries since the start-up launched in 2012, according to Sell.

Even Facebook servers never see the real shared pictures, offering no opportunity to save copies, target ads or collect data, said founder Nico Seller

The ultra-private messaging application lets people share messages or pictures that are encrypted in a way that doesn't even let Wickr see them. People also set how long they want messages to last before self-destructing.

HOW DOES IT WORK?

To use WTF, a user logs into Wickr, click the WTF tab, and can then take a photo or select an existing one.

The next step is to choose up to 151 friends to share it with. Those friends can view the photo within their Wickr feed before the are removed after 24 hours.

Users can also share the photo on Facebook. At first, the photo appears as a cat picture to every Facebook user.

But users, who have been pre-apporved, can double click on the photo and be redirected to Wickr to see the real image.

Versions of the application have been released for Android and Apple mobile devices as well as for computers powered by Macintosh, Windows or Linux software.

WTF was added to the free Wickr application made for Apple devices.

'We are taking a very complex spy tool, adding a joke and making it something my kids are going to use a hundred times a day,' Ms Sell said.

Wickr lets people post pictures at leading social network Facebook but, in a twist, uses an old-time spy technique called 'steganography.'

Ms Sell describes steganography as the art of hiding messages in plain sight. When Wickr pictures are posted to Facebook, what appears at the social network are adorable kitten photos instead of the personal images being shared.

WTF was inspired by Ms Sell's eldest daughter. The teenager wanted to connect with friends on Facebook but met resistance from her mum, who has been a long-time organiser of the infamous Def Con hacker gathering that takes place annually in Las Vegas.

WTF was inspired by Ms Sell's eldest daughter. The teenager wanted to connect with friends on Facebook but met resistance from her mum, who has been a long-time organiser of the infamous Def Con hacker gathering that takes place annually in Las Vegas

'She knows I don't like Facebook and asked mum to find a way to do it safely,' Ms Sell said of her concerns about privacy and control of personal information at popular social networks.

'This way, Facebook isn't going to control your photos; they will just see the kitty cat photos.'

Sell said that WTF may eventually do dog pictures, but as an in-app purchase. For now, kitten pictures will serve as the inside Wickr joke.

Worries about snooping by criminals, spies or governments have fueled interest in Wickr, according to Sell.

'We are the only secure messaging app that has not had a successful attack,' she said. 'We are the last man standing.'